You detect magical auras. The amount of information revealed depends on how long you study a particular area or subject.
1st Round

Presence or absence of magical auras.
2nd Round

Number of different magical auras and the power of the most potent aura.
3rd Round

The strength and location of each aura. If the items or creatures bearing the auras are in line of sight, you can make Spellcraft skill checks to determine the school of magic involved in each. (Make one check per aura; DC 15 + spell level, or 15 + half caster level for a nonspell effect.)

An aura’s power depends on a spell’s functioning spell level or an item’s caster level. If an aura falls into more than one category, detect magic indicates the stronger of the two.

Aura Power

Spell or Object

Faint

Moderate

Strong

Overwhelming

Functioning spell (spell level)

3rd or lower

4th-6th

7th-9th

10th+ (deity-level)

Magic item (caster level)

5th or lower

6th-11th

12th-20th

21st+ (artifact)

Lingering Aura

A magical aura lingers after its original source dissipates (in the case of a spell) or is destroyed (in the case of a magic item). If detect magic is cast and directed at such a location, the spell indicates an aura strength of dim (even weaker than a faint aura). How long the aura lingers at this dim level depends on its original power:

Original Strength

Duration of Lingering Aura

Faint

1d6 rounds

Moderate

1d6 minutes

Strong

1d6x10 minutes

Overwhelming

1d6 days

Outsiders and elementals are not magical in themselves, but if they are summoned, the conjuration spell registers.

Each round, you can turn to detect magic in a new area. The spell can penetrate barriers, but 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt blocks it.